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Reduction of Ti4+ to Ti3+ in Boron-Doped BaTiO3 at Very Low Temperature



Reduction of Ti4+ to Ti3+ was found in boron-doped BaTiO3 ceramics when we sintered the samples at very low temperature (>850°C) in 5%H2/Ar. Such reduction did not occur in pristine BaTiO3 ceramic. The methods such as UV–vis spectroscopy, luminescence spectroscopy, and X-ray photoelectron spectroscopy confirmed the reduction by showing the presence of Ti3+. The results of Ti–K-edge X-ray absorption near-edge structure measurement (XANES) indicated that boron doping changed the geometry of Ti-oxygen in BaTiO3 to some extent. It was likely that some boron ions stayed at interstitial sites of BaTiO3 lattice and acted as donors, which might trigger the reduction. The reduced boron-doped BaTiO3 were semiconducting and had very low room-temperature resistivity (<100 Ω m). However, different from the n-type rare-earth-doped BaTiO3 ceramics, they did not display positive temperature coefficient resistance (PTCR) behavior.